(1) Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same. Herein, the semiconductor device has a structure that a buffer coat film for preventing a filler attack by a seal resin is formed on a semiconductor substrate including a wiring layer insulated by an interlayer insulating film.
(2) Description of the Related Art
Recently, as a semiconductor integrated circuit is finely manufactured at high density, a wiring pitch between metal wires, such as power supply wires, formed on a semiconductor substrate becomes narrower. Therefore, a low-k film having a low dielectric constant is used for suppressing a parasitic capacitance of an interlayer insulating film. However, a low-k film is lower in withstand voltage and smaller in thickness than a conventional interlayer insulating film and, therefore, is finely formed as compared with a wiring pitch between metal wires. Hence, it is necessary and important to manage an apparatus and a method each used for preventing electrostatic discharge damage of an interlayer insulating film. Electrostatic discharge damage in a semiconductor device occurs as follows. That is, when static electricity in a human body or electricity charged by friction in a semiconductor device manufacturing step or a semiconductor device transferring step is discharged, high voltage in a range from several hundreds of volts to several thousands of volts is abruptly applied to an external input/output terminal, so that dielectric breakdown occurs at a gate oxide film, an interlayer insulating film and a metal wire. Thus, an integrated circuit suffers from operative failure. In order to prevent such electrostatic discharge damage, an external input/output terminal is provided with a protection circuit including a resistor and a diode in a CMOS device. As a result, an integrated circuit is protected from overvoltage to be applied thereto.
FIG. 7 is a circuit diagram illustrating one example of a conventional protection circuit in an external input terminal.
In the protection circuit illustrated in FIG. 7, a resistor 112 decreases applied high voltage to an applied noise level. Meanwhile, when current is supplied to a power supply (Vcc) line and a ground (GND) line through a protection diode 113 and a protection diode 114, respectively, a gate oxide film 111 is prevented from direct application of the discharged high voltage, so that a semiconductor device is protected. In such a protection circuit, however, the current flowing in the protection diode 113 and the protection diode 114 is limited in quantity; therefore, the protection diode 113 and the protection diode 114 suffer from junction damage in some cases if energy of applied noise is large. Herein, the resistor 112 typically has a resistivity in a range from 1 kΩ to 10 kΩ. Further, the resistor 112 takes a form of a diffusion layer or is made of polysilicon.
FIG. 8 is a sectional view illustrating a structure near an element electrode in a conventional semiconductor device.
As illustrated in FIG. 8, for example, the semiconductor device includes a semiconductor substrate 101, a plurality of element electrodes 104, a passivation film 105 and a buffer coat film 106. Herein, the semiconductor substrate 101 includes an interlayer insulating film 102 and a metal wire 103. Each of the plurality of element electrodes 104 is formed on the semiconductor substrate 101 to perform external signal input/output. The passivation film 105 having openings is formed on the semiconductor substrate 101. In each opening, the element electrode 104 is entirely or partially exposed. The buffer coat film 106 is formed on the passivation film 105 in order to prevent a filler attack by a seal resin. The buffer coat film 106 is typically made of an insulative organic material such as polyimide, and has a thickness of about several micrometers. Various films formed on the semiconductor substrate 101 have a thickness of several hundreds of nanometers. Therefore, it can be said that the buffer coat film 106 is very thick. Further, the buffer coat film 106 has a nature that negative electricity is readily charged on a surface thereof. Normally, the metal wire 103 is made of Al, Cu or the like.
In the conventional semiconductor device, as illustrated in FIG. 8, electricity is charged on the surface of the buffer coat film 106 on the semiconductor substrate 101 by static electricity generated in a semiconductor device manufacturing method or a semiconductor device manufacturing apparatus, so that a parasitic capacitance 107 is generated between the charged electricity and the metal wire 103. Due to the parasitic capacitance 107, the electricity is continuously charged on the surface of the buffer coat film 106. When the electricity is charged at a certain level, the parasitic capacitance 107 causes electric discharge at a position between the parasitic capacitance 107 and a nearest element electrode 104 adjoining thereto. Herein, a potential difference occurs at the relevant element electrode 104 by the parasitic capacitance 107. Due to the electric discharge, high voltage is applied to an internal circuit, and the resistor 112 and the protection diodes 113 and 114 in the conventional protection circuit illustrated in FIG. 7 cannot follow applied noise by the high voltage. Consequently, it is difficult to protect the gate oxide film 111. Further, if the applied voltage exceeds withstand voltage of the interlayer insulating film 102, the interlayer insulating film 102 is damaged and the metal wire 103 is fused, so that open/shortcircuit failure occurs between interlayer insulating films 102 or metal wires 103 in some cases. In a semiconductor device assembling step, most operations are performed in the air, and a semiconductor wafer is diced into semiconductor devices; therefore, each semiconductor device frequently suffers from an external electrical influence such as static electricity. In particular, electricity in a range from several hundreds of volts to several thousands of volts is charged on the surface of the buffer coat film 106 upon performance of back grinding or dicing. Therefore, static elimination by an ionizer is indispensable.
However, a diffusion process is subdivided in recent years. The low-k film serving as the interlayer insulating film 102 has a withstand voltage (not more than 106 V/cm) lower than that (107 V/cm) of a normal interlayer insulating film. In other words, the low-k film has lowered antistatic performance. Consequently, there arises a problem that a semiconductor device is damaged due to static electricity.